How much of a presence does Quentin Tarantino have in this film? I saw the preview and (probably to appeal to a U.S. audience) his character dominates. And not in a good way: his "acting" and lame Western accent is like pseudo-ironic camp. Dude really needs to stay behind a camera.

Not much. He had a part in the beginning and a few minutes in the middle. I laughed throughout the whole movie. Mostly for the bad English accents. But it was an enjoyable movie.